1Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, P.O. Box 49, Budapest H-1525, HungaryMelt-quenched amorphous Fe92-xBxZr7Cu1(2 less than or equal to x less than or equal to 23) ribbons were heat treated to the end of the first crystallization stage. The size of the BCC grains decreases from 20 to 6 nm with increasing B content, while the average thickness of the residual amorphous phase stays approximately constant at about 4 nm. The nanocrystalline BCC phase contains 2-4 at% of dissolved B and Zr, which is also reflected in its modified Curie temperature. The average composition of the residual amorphous regions in the nanocrystalline composite was established as Fe-2(B1-yZry), which makes possible a direct comparison of macro- and nanophases of close composition. (C) 2000 Elsevier Science B.V, All rights reserved.